Code refactoring to make NettyHttpClient the base class.
Make SSEClient private and extend from NettyHttpClient
Implement the interface of RxNetty’s HttpClient.
Remove unnecessary APIs. Javadoc updates.
Added static method to create HttpClient with custom pipeline configurator.
Merge pull request #91 from allenxwang/loadbalancer-refactoring

Code refactoring to have the NettyHttpClient implement HttpClient from RxNetty